The role of the many elements of chromosome structure in the processes of gene regulation in eukaryotes remains ambiguous. The importance of histones in a subunit structure of chromatin has been recently elucidated, but the functions of non-histones are largely unclear and the processes by which transcription is controlled remain unknown. Biochemical analysis of total cellular chromatin is inherently complex because of large numbers of chromosomal proteins on a wide range of DNA sequences. We propose to study the chromatin of a single gene in two eukaryotes in order to analyse its fine structure and regulation. The fine structure of the chromatin coding for ribosomal RNA (rRNA chromatin) will be observed by electron microscopy in the protozoan Tetrahymena and the acellular slime mold Physarum. In both organisms the genes coding for ribosomal RNA (rDNA) are organized in short extrachromosomal units and have a distinctive palindrome structure. The rRNA chromatin of Physarum will be purified from preparations of nucleoli in sufficient quantities to permit detection of proteins present only once per gene. The protein composition of the purified rRNA chromatin will be determined, and its structure observed by electron microscopy. The rRNA chromatin will be fractionated into defined fragments containing gene and spacer regions to localize proteins on these fragments. It is our long range aim to coordinate studies of fine structure with the functions of this gene and preliminary experiments are presented to investigate processes of transcription.